The general object of this invention is to permit the fabrication of an integrated optical circuit upon a substrate that includes a conventional thin-film or thick film electrical circuit including familiar integrated circuit (IC) chip devices. In the invention, a combination of electronic and optical circuits may be fabricated upon a same, common substrate.
The following references are cited to show the state of the art over which the devices and methods disclosed herein are considered an invention: Guha, A., et al. "Optical interconnections for massively parallel architectures" Appl. Optics, Volume 29, pp. 1077-1093, 1990; Goodman, J. W., et al. "Optical Interconnections for VLSI Systems", Proc. IEEE, Vol. 72, pp. 850-866, 1984; Hutcheson L. D. et al. "Optical Interconnects Replace Hard Wire", IEEE Spectrum, Vol. 24, 3 pp. 30-35, 1987; Kawachi, M., et al. "Flame Hydrolysis Deposition of SiO.sub.2 -TiO.sub.2 Glass Planar Optical Waveguides on Silicon"Jpn. J. Appl. Phys. Vol. 22, pp. 1932, 1983; Kawachi, M., et al. "Fabrication of SiO.sub.2 Glass Planar Optical Waveguides by Flame Hydrolosis Deposition", Electronics Letters, Vol. 19, 15 pp. 583-584, 1983; Mack, L. M. and Reisman, A., "Stress Measurements of Thermally Grown Thin Oxides on (100) S; Substrates", J. Electrochem. Soc. Vol. 136, No. 11, pp. 3433-3437, 1989; and, Bansal, N. and Doremus, R., Handbook of Glass Properties, Ch. 12, p. 363, 1986.
Flame hydrolysis deposition ("FHD"), a process which involves the deposit of powdered glass on a substrate and its subsequent fusion or consolidation into a solid glass at high temperatures, has been used to deposit waveguides for optical signal transmission on silicon and silica substrates. Such substrates, however, have not included thin film electrical circuits over which an FHD produced waveguide layer has been deposited. Other deposition methods such as chemical vapor deposition ("CVD") and sputtering have been used to form planar waveguides on substrates of silicon and silica. These latter methods have also not been used to deposit optical waveguides onto metalized Al.sub.2 O.sub.3 ceramic substrates or metalized silicon or silica substrates.
The device and method of the present invention involve the formation of optical waveguides on thin film or thick film wired, or metalized, Al.sub.2 O.sub.3, ceramic, silicon and silica substrates by using FHD techniques. In the present invention, a pretreatment coating is applied to the surface of the IC bearing substrate that includes thin or thick film wired, or metalized circuitry interconnecting IC chips. The pretreatment provides an interface between the metalized substrate which contains electrical circuits and the FHD glass layer which contains optical circuitry.
Thus, the purpose of the invention is to form optical waveguides on metalized substrates. In accordance, with this invention, optical waveguides and integrated optical circuits can be formed on a common substrate with IC chips to enable the integration of optical integrated circuits and electronic integrated circuits on the same component. A substrate may hold several IC chips between which thin or thick film wires provide signal transmission and electrical power. And optical circuitry in a glass layer superimposed over the substrate may similarly be operatively interconnected with the electronic circuitry. With this invention, the channel waveguides and integrated optical circuits can be formed in the glass layer, usually by known lithography and etching techniques. The waveguides of the present invention provide the optical interconnects which have been recently recognized as a promising solution to electrical interconnection bottlenecks in high speed electronics. The interconnection of optical circuitry and electrical circuitry is explained in greater detail in the Hutcheson article cited above which is incorporated by reference herein.
The optoelectronic chips that function with light received from a waveguide and correspondingly convert a light signal into an electronic signal, and vice versa, are known and electronic/optical converters are commercially available. The invention "integrates" an electronic integrated circuit with an optical integrated circuit on the same substrate unit as a single circuit module. Additional benefits of optical interconnections between electronic integrated circuits include immunity to electro-magnetic interference ("EMI") and the capability of various integrated optical circuits such as combiner/splitters, couplers, electro-optical circuits and non-linear optical circuits made from planar waveguides to be integrated with electronic integrated circuits on the same substrate.
With this invention, optical waveguides and circuits can be formed on thin film or thick film metalized, Al.sub.2 O.sub.3 ceramic and silicon and silica substrates. Because, Al.sub.2 O.sub.3 can withstand much higher process temperatures (up to 1600.degree. C.) than silicon or silica, the use of Al.sub.2 O.sub.3 ceramics permits higher process temperature in the deposition of the waveguide layer on the substrate. thus, an optical waveguide having a lower loss characteristic that is produced in a high temperature process can be deployed on a substrate including thin film or thick film metalized electrical interconnections.
In microelectronic device fabrication, in which IC chips are placed on metalized substrates to form a multi-chip circuit, the integrated optical circuits provided by the invention can be fabricated on the same substrate holding the multiple electronic IC chips. The invention is useful in making such opto-electronic devices for communication and computer industries.
In the present invention, a thin-film coating either silicon dioxide (SiO.sub.2) or silicon, is deposited onto the surface of a metalized substrate that may contain IC chips to (i) provide better adhesion of the subsequently deposited waveguide glass layer, (ii) prevent impurities in the substrate from adversely affecting the high purity glass used to form the waveguides during the deposition processes, and (iii) protect the metal film on the substrate from oxidization caused by oxygen penetration through the porous substrates and glass film. The thin-film coating between the substrate and the waveguides layer may be applied by sputtering, chemical vapor deposition (CVD), or other low temperature coating process. FHD is then used to deposit a glass layer on the pretreated substrate upon which the waveguides for the optical circuit are formed.
The foregoing and other objects and advantages of the invention will become more apparent when considered in view of the accompanying drawings and the following descriptions: